This invention relates to a method for forming a load-carrying pile, and in particular to a method for forming a pile by driving a thin-walled pipe.
A load carrying pile can be formed by driving a hollow pipe into the ground, filling the pipe with fluid concrete and allowing the concrete to cure. For this pile-forming method, a thin-walled pipe is less expensive to use than a pipe having a more substantial wall thickness. However, pipe used to form such a pile must have a wall thickness sufficient to withstand the force required to drive the pipe into the ground. Typical methods of driving pipe do not permit the use of thin-walled pipe because such pipe fails, or collapses, before it can be driven to a sufficient depth or refusal bearing.
U.S. Pat. No. 2,779,161 to Pickman discloses a method for constructing a pile by driving a pipe into the ground by means of a drop hammer rammer which strikes a concrete plug located at the lower, or driving, end of the pipe, after which the pipe is filled with concrete. Japanese Patent Publication No. 57-151729 discloses a similar method including filling the tip of a pipe with concrete, hardening the concrete, placing a buffer such as sand on the concrete and driving the pipe by using a drop hammer rammer to strike the buffered concrete. However, each of these methods is limited to use with a drop hammer and short sections of pipe, for example 40-foot sections, which is inherently slow. Use of a powered hammer (air-diesel, etc.) and mandrel for driving longer pipes would be faster, but is impractical in view of the excessively long mandrel required if longer pipes are used.
In addition, by using a bottom-driven short concrete plug, there is a chance of driving the plug out the bottom due to increased frictional resistance on the exterior of the pipe as the pipe drives deeper. Japanese Patent No. 57-151729 suggests the use of spiral pipe to resist expulsion of the plug by the raised bead (weld-padding) formed when the steel plate (2 to 3 feet wide) is welded together in a spiral. Most available pipe, however, is seamless and could not prevent expulsion of the plug in this manner.
U.S. Pat. No. 3,779,025 to Godley et al. discloses a method of installing a pile by driving a length of pipe into the ground, filling the pipe completely with concrete, curing the concrete and then driving the pipe further into the ground to a final bearing depth. However, since the pipe must be filled completely with concrete to enable completion of driving, much concrete and pipe are wasted whenever a substantial undriven portion of the pipe remains above ground and must be cut off when the pipe has been driven to final bearing depth.